An all-solid-state lithium battery using inorganic solid electrolytes requires safety assurance and improved energy density, both of which are issues in large-scale applications of lithium-ion batteries. Utilization of high-capacity lithium-excess electrode materials is effective for the further increase in energy density. However, they have never been applied to all-solid-state batteries. Operational difficulty of all-solid-state batteries using them generally lies in the construction of the electrode-electrolyte interface. By the amorphization of Li2RuO3 as a lithium-excess model material with Li2SO4, here, we have first demonstrated a reversible oxygen redox reaction in all-solid-state batteries. Amorphous nature of the Li2RuO3-Li2SO4 matrix enables inclusion of active material with high conductivity and ductility for achieving favorable interfaces with charge transfer capabilities, leading to the stable operation of all-solid-state batteries.

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glasses were synthesized by a mechanochemical technique. The glasses were heat treated to obtain the glass-ceramics. Raman spectra indicated that these glasses were composed of ortho-borate, carbonate and lithium ions. After milling, a solid solution based on Li 2 CO 3 was obtained at the 20Li 3 BO 3 ·80Li 2 CO 3 composition. By heating the milled sample at 500°C, the crystallinity and conductivity increased. This heated sample showed the conductivity of 1.2 © 10 ¹6 S cm ¹1 at room temperature, which is eight orders of magnitude higher than that of Li 2 CO 3 crystal.

To improve the ionic conductivity of solid electrolytes, it is generally thought that anions with high polarizability should be used. However, the relationship between polarization and conductivity is not clear because conductivity largely depends on the crystal structure. In this study, we focus on amorphous materials with no long-range ordered structure. The conductivity and ductility properties of lithium boron oxide (Li3BO3), lithium boron nitride (Li3BN2), and lithium boron sulfide (Li3BS3) are compared. Li3BS3 glass is prepared from Li2S, B, and S using heat treatment and a mechanochemical process. It has high ductility and a higher ionic conductivity (3.6 × 10–4 S cm–1 at 25 °C) than that of Li3BO3 and Li3BN2 glass with a low activation energy of 32 kJ mol–1. Li3BS3 glass is therefore suitable as an ionic conductor with high conductivity. The electronegativity of anions and glass properties such as ionic conductivity and ductility are correlated, and it is proposed that this relationship can be used as a basis for investigating fast ionic conductors.

Amorphous LiCoO2-based positive electrode materials are synthesized by a mechanical milling technique. As a lithium oxy-acid, Li2SO4, Li3PO4, Li3BO3, Li2CO3, and LiNO3 are selected and milled with LiCoO2. XRD patterns indicate that reaction between LiCoO2 and these lithium oxy-acids proceeds. Amorphization mainly occurs, and several broad peaks attributable to cubic LiCoO2 are observed in all the samples. These amorphous active materials show mixed conductivities of electron and lithium ion. All-solid-state cells using the prepared amorphous active materials and the Li2.9B0.9S0.1O3.1 glass-ceramic electrolyte are fabricated and their charge-discharge properties are examined. The cells with only the 80LiCoO2·20Li2SO4 (mol%) and the 80LiCoO2·20Li3PO4 active materials function as secondary batteries. This is because higher lithium ionic conductivities are obtained in the 80LiCoO2·20Li2SO4 and 80LiCoO2·20Li3PO4 active materials than in the others. The largest capacity is obtained in the cell with the 80LiCoO2·20Li2SO4 active material because of its good formability and high lithium ionic conductivity. In addition, the cell with the 80LiCoO2·20Li2SO4 positive electrode active material shows the better cycle and rate performance than that with the crystalline LiCoO2. It is noted that the amorphization with lithium oxy-acids is a promising technique for achieving a novel active material with better electrochemical performance.

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Low-melting oxide glasses are promising as electrolytes for all-solid-state lithium rechargeable batteries. Glasses in the pseudobinary system Li 3 BO 3 Li 2 SO 4 were prepared by a mechanochemical technique. Raman spectra revealed that the glasses contained no macroanions which form networks but consisted only of Li + ions and two discrete ortho-oxoanions, BO 3 3¹ and SO 4 2¹. The density and molar volume increased and elastic moduli decreased with an increase in the Li 2 SO 4 content in the glasses. The heat treatment of the Li 3 BO 3 Li 2 SO 4 glasses at around 300°C brought about the crystallization to form ion conducting glassceramics. Electrical conductivities of the glasses and glass-ceramics in this system were maximized with the mixing of Li 3 BO 3 and Li 2 SO 4 . The conductivities were higher in the glass-ceramics of the compositions with small amounts of Li 2 SO 4 , ranging from 3 © 10 ¹6 to 1 © 10 ¹5 S cm ¹1 at room temperature, compared to the corresponding glasses. This conductivity enhancement by the heat treatment is probably due to the precipitation of solid solutions with a high temperature Li 3 BO 3 phase.